Adsorption before Langmuir.

Before the ground breaking development of the Langmuir equation observations and experimentation involving absorbance at surfaces took two approaches. The first involved components at the interface between, primarily water and air, the second approach involved the exchange of ions when solutions passed though soil or a zeolite. In the first case, the interaction of compounds having a hydrophilic end and a hydrophobic end with water were extensively studied. It was found that when the area available to these compounds was decreased they would arrange in such a way as to have the hydrophobic end in air and the hydrophilic end in water thus forming a monolayer. From this monolayer, it is possible to calculate Avogadro’s number. The other approach is primarily attributed to Thompson and Way who described the exchange of one ion for another when a solution of ions was passed through soil. This activity was later attributed to soil zeolites. Both of these lines of intensive and extensive investigation led to a great deal of knowledge about these two phenomena. However, it was not until the development of the Langmuir equation that the concept of a specific site responsible to the attachment of these components was developed and codified into a mathematical equation.